Extrapancreatic extension is a better adverse prognostic factor than tumor size in patients with localized pancreatic ductal adenocarcinoma treated with chemoradiotherapy - comparison of T category between the American Joint Committee on Cancer and Japan Pancreas Society.

Background: T category classification for pancreatic ductal adenocarcinoma (PDAC) in the Classification of Pancreatic Cancer by the Japan Pancreas Society (JPS) is quite different from that of the American Joint Committee on Cancer (AJCC). The JPS classification focuses on extrapancreatic extension, while the AJCC focuses mainly on tumor size. This study aimed at identifying prognostic factors in PDAC patients undergoing chemoradiotherapy (CRT) by comparing the differences of T categories in these two classifications.

Methods: This retrospective study involved 344 PDAC patients who underwent CRT from 2005 to 2019 and their T-category variables were re-evaluated on computed tomography (CT) images. Disease-specific survival (DSS) was compared based on the JPS and AJCC T categories, while multivariate analysis was performed to identify prognostic factors.

Results: Based on the AJCC, 5-year DSS of T3 was better than those of T1 and T2 (57.1% vs. 47.7% and 37.4%). In multivariate analysis, performance status, CEA, the involvement of superior mesenteric vein and superior mesenteric artery, the JPS stage before CRT, and regimen of chemotherapy were identified as independent prognostic factors.

Conclusions: In localized PDAC patients treated with chemoradiotherapy, extrapancreatic extension, as while as biological, conditional and therapeutic factors, is a better prognostic factor than tumor size.